use std::env; fn main() { println!("cargo:rerun-if-changed=build.rs"); let opt_level = env::var("OPT_LEVEL") .ok() .and_then(|s| s.parse().ok()) .unwrap_or(0); let profile = env::var("PROFILE").unwrap_or_default(); if profile == "release" || opt_level >= 2 { println!("cargo:rustc-cfg=optimized"); } }